The present invention relates generally to artificial neurons, and more particularly to a method and circuitry for closely simulating both the known and theoretical functioning of a biological neuron and more importantly, for simulating the neuron's function of learning.
A neuron is a single nerve cell and is the basic building block of the biological nervous system. Each individual neuron is adapted to receive stimuli in the form of electrical pulses from various sources including other neurons and receptor sense organs such as the eyes and ears. Neurons receive these stimuli through their inputs, which are called synapses, and respond to these stimuli by generating electrical output signals in the form of pulses which may in turn be utilized as stimuli to other neurons or to control effector organs such as muscles.
In the past, attempts have been made to simulate the behaviour of neurons with electronic circuitry. As an example of such a circuit, U.S. Pat. No. 3,351,773, to Wolf et al, discloses an artificial neuron circuit which, like actual neurons, has a plurality of inputs, or synapses, the potential of which are summed together and cause the neuron to generate an output, or "fire", if and when their sum exceeds a certain threshold potential. However, in order properly to simulate the operation of an actual neuron, the artificial neuron must exhibit the ability to learn. As will be shown later, biological neurons learn by altering the manner in which they react to stimuli according to a variety of temporal and spatial parameters. The artificial neuron set forth by Wolf does not have this ability and as such, is not capable of learning.
There have been attempts at devising artificial neurons which do possess a learning ability. One such neuron device is disclosed in U.S. Pat. No. 3,496,382, to Hendrix. This patent sets forth a neuron circuit in which the threshold potential of the neuron is alterable, depending upon whether action which results when the neuron fires is desirable or undesirable. Specificially, if the firing of the neuron causes a desirable action, the neuron's threshold will be lowered so that it can more easily fire, whereas if this action is undesirable, the threshold of the neuron will be raised so that it will be less likely to fire.
Although the Hendrix patent attempts to simulate the learning function of a neuron, the circuit, like that of the Wolf patent, suffers drawbacks. As will be shown, the actual process by which a neuron learns is very complex and the simple manner in which the Hendrix patent attempts to replicate it by varying the threshold potential does not provide an accurate simulation of this important function of a neuron.